Pennsylvania owners of Ford's 2013 Fusion Hybrid and C-Max Hybrid cars are suing the Detroit auto company because their vehicles are falling far below the advertised 47 mpg. In fact, they've fallen as short as 17 to 21 percent below that figure.

The lawsuit, which was filed by Pennsylvania owners of the two vehicles in Philadelphia federal court, seeks damages of at least $5 million and says Ford has violated the state’s unfair-trade practices and consumer protection laws.

“Plaintiffs are some of the tens of thousands of consumers who purchased a Fusion Hybrid or C-Max Hybrid, only to be stuck with under-performing, less valuable vehicles that inflict higher fuel costs on their owners,” according to the complaint.

Back in December 2012, Consumer Reports pointed out the inaccuracies of both the 2013 Fusion Hybrid and C-Max Hybrid cars. According to its testing, the C-Max Hybrid received 35/38/37 mpg for city/highway/combined and the Fusion Hybrid had 35/41/39 mpg.

At that time, Ford responded to Consumer Reports' claims saying that mileage varies among hybrids.

"Early C-Max Hybrid and Fusion Hybrid customers praise the vehicles and report a range of fuel economy figures, including some reports above 47 mpg," said Ford spokesman Wes Sherwood. "This reinforces the fact that driving styles, driving conditions and other factors can cause mileage to vary."

While all vehicles must undergo the EPA test for fuel efficiency, the test isn't actually administered by the government agency. Instead, automakers perform the test and the EPA reviews it. In many cases, factors like temperature and speed result in gas mileage being lower than the EPA sticker.

But after Ford was called out for coming up with inaccurate fuel ratings for its two hybrids, the EPA stepped in to do a test of its own.

In another round of testing of the C-Max Hybrid in March, Wayne Gerdes found that it only achieved 35.537 miles per gallon over 360 highway miles. But in the city, he was able to achieve 52 miles per gallon over 22.8 miles of driving, which is better than the EPA promises.

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